1. Field of the Invention
The present invention generally relates to a wireless electric power receiver, and more particularly to a wireless electric power receiver for wirelessly receiving electric power based on an electromagnetic resonance scheme.
2. Description of the Related Art
A mobile terminal, such as portable telephones and Personal Digital Assistants (PDA), is typically operated by a rechargeable battery. In order to charge the battery, the battery of the mobile terminal is supplied with electric energy by using a separate charging device. Typically, the charging device and the battery have separate contact terminals on an exterior thereof, respectively, and are electrically connected with each other by the contacting their contact terminals.
However, in the contact type charging method, since the contact terminals protrude toward an exterior, the contact terminals may be easily damaged or become dirty due to alien substances. As a result, there is problem in that the charging of the battery is not properly performed. Where the contact terminals are exposed to moisture, the charging of the battery may not be properly performed.
In order to solve the above mentioned problems, wireless charging technologies or noncontact charging technologies have been recently developed and utilized for many electronic devices.
In the wireless charging technologies, wireless electric power transmission and reception techniques are used. For example, when a portable terminal is not connected to a separate charging connector and merely put on a charging pad, a battery of the portable terminal is automatically charged. The wireless charging technologies have advantages in that electronic products are wirelessly charged resulting in an improvement of a waterproof function, and the portability of electronic devices can be improved because a wired charging device is unnecessary. Further, it is forecasted that related technologies will significantly grow in the coming electric vehicle era.
The wireless charging technologies generally include an electromagnetic induction scheme using a coil, a resonance scheme using resonance, and an RF/Micro wave radiation scheme in which electric energy is converted into microwaves and then transmitted.
Up to now, the electromagnetic induction scheme has become mainstream. Recently, domestic and foreign experiments have been successful in using microwaves at distances of several tens of meters to wirelessly transfer electric power. In the near future, it is expected that all electronic products will be wirelessly charged without electric wires anywhere and anytime.
Transfer of electric power using electromagnetic induction is a scheme that transfers electric power between a first coil and a second coil. When a magnet is moved in a coil, induction current occurs. By using the induction current, a magnetic field is generated at a transferring end, and electric current is induced according to a change of the magnetic field so as to create energy at a reception end. This is referred to as magnetic induction phenomenon, and a method of transferring electric power using magnetic induction has remarkable energy transfer efficiency.
In the resonance scheme, a system for wirelessly transferring electricity by using the electric power transfer principle at a distance of several meters from a charging device in a Coupled Mode Theory has been developed. This wireless charging system resonates electromagnetic waves, and since a part of the resonated electric energy is directly transferred to a device having an identical resonance frequency when the device having the identical resonance frequency appears, and residual waves are absorbed again into an electromagnetic field without a distribution in air, it seems that the resonated electric energy has no effect on a peripheral machine or the human body different from other electromagnetic waves.
On the other hand, a wireless electric power receiver using a conventional resonance scheme includes a rectifier circuit for converting received alternating current waves into direct current waves, and a DC-DC conversion circuit for regulating electric power of the rectified direct waves to a predetermined voltage value. However, because the DC-DC conversion circuit must use a manual element with a large external value, there is a difficulty in that the circuit is implemented to have a small mounting surface, a high capacity and a high efficiency. In a case where the wireless electric power receiver is implemented in a mobile communication device, an increase of the mounting surface has a negative effect on the thickness of the mobile communication device.